The basic principle of bleeding ATV brakes is relatively straightforward. But getting the brakes to bleed properly may sometimes be easier said than done. This post addresses the most common reasons your ATV brakes won’t bleed and how to fix them.
You always get the best result from combining these methods to ensure all the air is out of the system.
1. There is air trapped in the banjo bolt
The standard brake bleeding methods will usually eliminate all the air trapped inside the brake lines. But air may still be trapped inside the connector that attaches the brake line to the master cylinder, often called “a banjo bolt.”
To relieve this air, you need to engage the hand lever while briefly loosening the nut holding the banjo in place.
Tighten the nut before the lever bottoms out. I recommend using a rag to soak up the brake fluid that squirts out so that it won’t damage the paint on your bike.
2. Not enough fluid being pumped from the master cylinder
The master cylinder on ATVs and the piston inside are relatively small compared to the ones you find on cars or other larger vehicles. Because of its small size, it can only pump a relatively small amount of brake fluid with each pump.
This makes the standard method of bleeding brakes work less efficiently on smaller brake systems found on ATVs, UTVs, dirt bikes, motorcycles, or snowmobiles.
The amount of fluid being pumped might not be sufficient to expel the air bubbles before you bottom out and need to start a new pumping cycle.
3. The brake shoes are not adjusted properly
Before bleeding your hydraulic drum brakes, you must adjust the brake shoes correctly. You will never get a good brake feel if they are not snug.
Adjust the shoes according to factory specifications. The adjuster on each side must be adjusted equally, and the brake shoes must rub the drums quite a bit.
You should feel a noticeable drag when you turn the hub. If they are just barely scraping, you may have problems bleeding the brakes properly as the slave cylinder won’t be able to push the shoes far enough.
4. There is a leak somewhere in the brake system
Even the tiniest leak may be enough to prevent you from achieving firm brakes. Check the whole system with a dry paper towel, and address any found leaks.
5. There is air trapped in the master cylinder
To remove the air trapped inside the master cylinder, you need to perform a bench bleeding procedure.
The process of bench bleeding the master cylinder is a bit more comprehensive than just standard brake bleeding, but sometimes it is necessary to remove the air trapped inside.
If you happened to run the brake fluid reservoir dry or have replaced or rebuilt your master cylinder, there is a good chance air trapped in the master cylinder is the cause of your problems.
I’ve dedicated a separate post on how you may bleed the master cylinder.
6. The master cylinder is bad
If you struggle to get the fluid down the brake lines, chances are your master cylinder has gone bad.
Inside the cylinder, you find a plunger with an o-ring that tends to wear or go bad over time. If you need to pump the brakes several times to make them firm, this indicates that your master cylinder has gone bad.
Luckily you can rebuild an old master cylinder, and the parts needed do not cost much. Most manufacturers sell kits that fit your specific unit with step-by-step instructions.
7. Incorrect handle installed
If you happened to replace your brake handle/lever recently, it might be what is causing you trouble.
Installing an aftermarket lever or the wrong type may prevent the piston inside the master cylinder from fully retracting when the lever is released.
This may, in turn, prevent the brake fluid from flowing down and in front of the piston. The piston will move, but it won’t get any fluid from the reservoir to pump down the brake lines.
8. Missing copper washers by the banjo bolt
If you have opened the banjo bolt previously, make sure you installed it correctly with one copper or aluminum washer on each side.
If assembled incorrectly, you may have problems building up the pressure, or you may suck air into the brake system each time you pump the brakes.
9. Clogged brake line or bleeder screws
Over time, your brake lines may get clogged by corrosion and debris. If you cannot press one drop of fluid out of an open bleeder valve or the brake fluid flow is weak, you may have a clogging issue.
Try disconnecting the banjo connector from your master cylinder and pump the brake to see if the cylinder is working correctly. Use a rag to prevent the corrosive brake fluid from ruining your paint and plastic.
If you get a firm squirt of brake fluid when you press the brake lever, the clogging is likely somewhere in your brake line.
Before replacing brake lines, it’s worth completely removing the bleeder valve to see if this clears things up. Replace clogged bleeder valves with new ones. Bring the old one for reference to your local automotive store. New bleeder valves are usually cheap.
Additional tips for stubborn brakes that will not bleed
I’ll finish with many last-resort tips to try if your brakes seem in good shape but do not want to bleed.
Leave the brake lever engaged overnight
A simple trick to try out if you have tried everything and do not want to start messing with the master cylinder is to zip tie or rubber band the lever in the engaged position overnight.
If you are lucky, this may be all it takes to let the most stubborn bubbles of air escape into the reservoir tank.
Slowly pump the brakes with the master cylinder cover off
Here is one more simple trick to try before you attempt a complete master cylinder bleed.
Open the brake fluid reservoir cover. With the reservoir topped off with brake fluid and all the bleeder valves closed, slowly begin pumping the brakes. Note if you see any bubbles appearing in the reservoir.
Continue pumping until there are no more bubbles. Reinstall the cover and test your brakes.
Gravity-bleed the brakes
Gravity bleeding is a well know method to try when everything else fails. It may or may not be effective. The only way to find out is to try it out.
- Start by removing the brake fluid reservoir cover, and top it off with fluid.
- Put trays under each brake caliper and open the bleeder valves.
- Leave the system for about 20 minutes. Ensure the reservoir does not run dry, or you will be in for a much harder bleeding job.
- Add more fluid when it is starting to run low.
- Brake fluid will drip out slowly through the bleed valves. Hopefully, the air will come out with the fluid as well.
- After topping off the reservoir a few times, you may try tightening the bleeder valves, replacing the reservoir cover, and see if the brakes have improved.
When The brakes will still not bleed
If you have reached this point and still had no success bleeding your brakes, I salute your willpower!
Try over-filling the brake fluid reservoir.
One time, I had no luck bleeding the brakes on my KTM EXC dirt bike. I tried everything and used bottle after bottle of brake fluid. The brakes were still soft.
Then I tried topping off the brake fluid reservoir completely before continuing manually pumping and bleeding the brakes. And what do you know, after just a few pumps, the brakes were rock solid again.
I cannot explain how it happened, but consider giving it a shot before giving in and taking your ATV to the dealer.
There you have it – everything you need to roll up your sleeves and get your ATV brakes bleeding right. Remember, it’s okay if it doesn’t work out the first time; even seasoned mechanics face challenges with this. But with the tips from this article in your toolbox, you’re well on your way to getting those brakes working smoothly again.